In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 .mu.m range, a cleanliness class of 100-1000 (which means the number of particles at sizes larger than 0.5 .mu.m per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 .mu.m, a cleanliness class of 0.1 is required. It has been recognized that an inert minienvironment may be the only solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness minienvironment that is constantly flush with ultrapure nitrogen that contains no oxygen and moisture.
Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new minienvironment concept which is shown in FIG. 1. Within the enclosure of the minienvironment of a process tool 10, an extremely high cleanliness class of 0.1 (which means the number of particles at sizes larger than 0.1 .mu.m per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area 12. In order to maintain the high cleanliness class inside the process tool 10, the loading and unloading sections 14 of the process tool must be handled automatically by an input/output device such as a SMIF (standard mechanical interfaces) apparatus. A cassette or wafer can be transported into the process tool 10 by SMIF pod 18 situated on top of the SMIF apparatus 20.
In a conventional SMIF apparatus 20 such as that shown in FIG. 1, the apparatus 20 consists of a robotic arm which is normally configured for gripping the top of a cassette 30 from a platform on which the cassette 30 is placed (inside a pod). The robotic arm, sometimes replaced by a gripper assembly, is capable of transporting the cassette 20 into the process tool and place it onto a platform 16 vertically such that the cassette 30 is oriented horizontally. At the beginning of the process, an operator positions a SMIF pod 18 on top of a platform/elevator 22 which contains a cassette 40 holding, for instance, 24 wafers in an upright position. The elevator then descends into the SMIF apparatus 20 for the robotic arm to transport cassette 30 into the process tool. The SMIF system 20 is therefore capable of automatically utilizing clean isolation technology to maintain a high class clean room effectiveness near wafers and processing equipment. The operation of the robotic arm or the gripper is controlled by an ancillary computer (not shown) or by the process tool 10. The cassette 30 carries wafers or other substrates that are being processed.
Also provided in the clean room is a central vacuum system (not shown) equipped with vacuum outlet 40 as shown in FIG. 1. The vacuum outlet 40 is constructed by a vacuum conduit 42 and a cover assembly 44. The central vacuum system is provided with vacuum outlet 40 throughout a clean room, and is normally installed in the clean room floor such that a top surface of the cover assembly 44 is flush with the top surface 32 of the clean room floor. The purpose of the central vacuum system is to provide ready access to a factory vacuum source for cleaning of processed tools or process machines.
The cover assembly 44 for the central vacuum outlet 40 is further shown in FIGS. 1B-1D. FIG. 1B is a perspective view of a cover assembly 44 positioned on top and spaced apart from the vacuum conduit 42. The cover assembly 44 is normally provided with a recess 34 in a top surface 36 of the cover assembly 44. The recess 34 is further provided with a pin 38 for grasp by a pair of pincers during a preventive maintenance procedure. The cover assembly 44 is constructed by an upper portion 46 and a lower portion 48 that are both formed in an annular shape. The outside diameter of the lower portion 48 is smaller than the inside diameter of the conduit 42 such that a snug fit can be achieved for a vacuum-tight seal. FIG. 1C illustrates a plane view of the cover assembly 44, while FIG. 1D illustrates a cross-sectional view of the cover assembly 44.
The cover assembly 44 illustrated in FIGS. 1A-1D serves the purpose of sealing a vacuum outlet 40. However, whenever an operator needs to use the vacuum by attaching a hose connector to the conduit 42, a pair of pincers or Allen wrench must be used to pick up the cover assembly 44 by the pin 38. This process must be repeated several times a day whenever the process chamber, or the process machine needs to be cleaned. To facilitate the removal of the cover assembly 44, other attempts have been made such as tying a cable tie to the pin 38 so that the cover assembly 44 can be picked up by pulling on the cable tie. However, the cable tie arrangement can produce particle contaminations for the clean room environment. It is therefore highly undesirable to introduce a foreign object for picking the cover assembly 44, i.e. either by a tool or by a cable tie that is tied to the cover assembly 44.